// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// http://code.google.com/p/protobuf-j2me/
//
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package com.google.protobuf;

/**
 * <p>
 * An {@code RpcController} mediates a single method call. The primary purpose
 * of the controller is to provide a way to manipulate settings specific to the
 * RPC implementation and to find out about RPC-level errors.
 * 
 * <p>
 * Starting with version 2.3.0, RPC implementations should not try to build on
 * this, but should instead provide code generator plugins which generate code
 * specific to the particular RPC implementation. This way the generated code
 * can be more appropriate for the implementation in use and can avoid
 * unnecessary layers of indirection.
 * 
 * <p>
 * The methods provided by the {@code RpcController} interface are intended to
 * be a "least common denominator" set of features which we expect all
 * implementations to support. Specific implementations may provide more
 * advanced features (e.g. deadline propagation).
 * 
 * @author kenton@google.com Kenton Varda
 */
public interface RpcController {
  // -----------------------------------------------------------------
  // These calls may be made from the client side only. Their results
  // are undefined on the server side (may throw RuntimeExceptions).

  /**
   * Resets the RpcController to its initial state so that it may be reused in a
   * new call. This can be called from the client side only. It must not be
   * called while an RPC is in progress.
   */
  void reset();

  /**
   * After a call has finished, returns true if the call failed. The possible
   * reasons for failure depend on the RPC implementation. {@code failed()} most
   * only be called on the client side, and must not be called before a call has
   * finished.
   */
  boolean failed();

  /**
   * If {@code failed()} is {@code true}, returns a human-readable description
   * of the error.
   */
  String errorText();

  /**
   * Advises the RPC system that the caller desires that the RPC call be
   * canceled. The RPC system may cancel it immediately, may wait awhile and
   * then cancel it, or may not even cancel the call at all. If the call is
   * canceled, the "done" callback will still be called and the RpcController
   * will indicate that the call failed at that time.
   */
  void startCancel();

  // -----------------------------------------------------------------
  // These calls may be made from the server side only. Their results
  // are undefined on the client side (may throw RuntimeExceptions).

  /**
   * Causes {@code failed()} to return true on the client side. {@code reason}
   * will be incorporated into the message returned by {@code errorText()}. If
   * you find you need to return machine-readable information about failures,
   * you should incorporate it into your response protocol buffer and should NOT
   * call {@code setFailed()}.
   */
  void setFailed(String reason);

  /**
   * If {@code true}, indicates that the client canceled the RPC, so the server
   * may as well give up on replying to it. This method must be called on the
   * server side only. The server should still call the final "done" callback.
   */
  boolean isCanceled();

  /**
   * Asks that the given callback be called when the RPC is canceled. The
   * parameter passed to the callback will always be {@code null}. The callback
   * will always be called exactly once. If the RPC completes without being
   * canceled, the callback will be called after completion. If the RPC has
   * already been canceled when NotifyOnCancel() is called, the callback will be
   * called immediately.
   * 
   * <p>
   * {@code notifyOnCancel()} must be called no more than once per request. It
   * must be called on the server side only.
   */
  void notifyOnCancel(RpcCallback callback);
}
